Honeycomb core material for sandwich structure and method for manufacturing the same

ABSTRACT

A honeycomb core material which is excellent in flame retardation, thermal insulation and noise insulation and has improved transportability and handling efficiency and which can be suitably used also for a sandwich structure of a curved shape as a foam has flexibility and elasticity, and a method for its production. 
     A composite foam comprising a phosphoric acid type inorganic foam and a urethane type organic foam, obtained by foaming and curing an aqueous mixture containing a phosphorus-containing acid material, a curing agent, a blowing agent and a urethane polymer having NCO groups, is filled in cells of a honeycomb body having a cell size of from 3 to 100 mm and a porosity of from 92 to 99.5% according to JIS-A6931.

TECHNICAL FIELD

The present invention relates to a honeycomb core material for asandwich structure and a method for its production.

BACKGROUND ART

Heretofore, a sandwich structure having a honeycomb core materialsandwiched by rigid surface materials made of e.g. a steel plate, hasbeen widely used as an interior or exterior panel for a buildingmaterial such as a door or a partition, or as a material for a structuresuch as an aircraft or a vehicle, since it is excellent in suchcharacteristics as light weight, rigidity, sound absorption and thermalinsulation. In order to improve the sound absorption or thermalinsulation among such various characteristics of the structure, ahoneycomb core material having a resin foam filled in cells of thehoneycomb body, has also been known.

However, with a conventional honeycomb core material having a resin foamfilled, the resin foam filled in cells was hard and brittle, and ifbending occurred by e.g. transportation, the foam was likely to slip offfrom the cells, and consequently, the transportability or handlingefficiency was poor. Further, in a state where the resin foam was notfilled over the entire cells of the honeycomb core material, the thermalinsulation of the honeycomb core material was non-uniform or poor.Therefore, JP-A-1-301329 proposes to prevent slipping off of the foam byproviding a notch at one end of the cell wall of the honeycomb corematerial. However, in this case, the partition wall was not continuous,and there was a problem that the mechanical strength, particularly theshear strength, was poor.

On the other hand, PCT publication WO97/11925 discloses a foam of aphosphorus-containing acid material as one which is excellent innon-combustibility and fire proof property and whereby the foam can bemolded under ordinary temperature and ordinary pressure conditions.However, such a foam was flexible and had elasticity, and by itself, itwas sometimes inadequate as a structure whereby rigidity was required.

An object of the present invention is to provide a honeycomb corematerial whereby a resin foam is flexible and has elasticity whilemaintaining the thermal insulation and noise insulation of a honeycombcore material having a conventional resin foam filled, and which issuitable for a sandwich structure having improved transportability andhandling efficiency and useful also for a curved sandwich structure, anda method for its production.

DISCLOSURE OF THE INVENTION

The present invention has been made to accomplish the above object.Namely, the present invention resides in a honeycomb core material for asandwich structure, which comprises a honeycomb body and a filler filledin at least a part of cells thereof, wherein the honeycomb body has acell size of from 3 to 100 mm and a porosity of from 92 to 99.5%, asstipulated in JIS-A6931, and the filler is a composite foam comprisingan inorganic foam obtained from a phosphorus-containing acid material(a), a curing agent (b) and, if necessary, a blowing agent (c), and anorganic foam obtained from a urethane prepolymer having NCO groups (d),and water (e).

Further, the present invention resides in a method for producing ahoneycomb core material for a sandwich structure, which comprisesfilling a mixture comprising a phosphorus-containing acid material (a),a curing agent (b), a urethane prepolymer having NCO groups (d), water(e) and, if necessary, a blowing agent (c), in cells of a honeycomb bodyhaving a cell size of from 3 to 100 mm and a porosity of from 92 to99.5%, as stipulated in JIS-A6931, followed by foaming and curing.

Such a honeycomb core material according to the present invention isexcellent in flame retardation or non-flammability which can not beattained by a conventional organic foam and is flexible and haselasticity, which can not be obtained by a conventional inorganic foam,as the filler in its cells is composed of the above-mentioned inorganicand organic composite foam. In addition, according to the discovery bythe present inventors, it has been found that when components to formsuch a composite foam, are foamed and cured in cells of the honeycombbody, the foaming and expansion force of the foam bring about anextremely high adhesiveness between the honeycomb and the filler incombination with the inherently high adhesiveness of a urethane polymer.

The honeycomb core material of the present invention is thereby freefrom slipping off of the filler from the honeycomb body and easy intransportation or handling, and also has flexibility and modification inshape after the production is possible, whereby surface materials suchas flat plates can easily be attached to the honeycomb core material,and it becomes possible to apply it to a structure having a curvedshape.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows perspective views of some typical examples of the honeycombbody to be used for the honeycomb core material of the presentinvention. In these examples, the cells have the following shapes. (1)hexagonal shape, (2) circular shape, (3) cardboard shape, (4) rib shape,and (5) origami shape.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the present invention will be described in further detail.

The honeycomb body to form the honeycomb core material of the presentinvention has a conformation having substantially continuous geometricalcells (through holes) of a polygonal shape such as a hexagonal shape, atetragonal shape, or a triangular shape, a circular shape or aninequilateral polygonal shape, defined by partition walls made of acontinuous member. The cell size and the porosity of the honeycomb bodyrelate to the rigidity of the honeycomb core material to be produced,and they are stipulated by JIS-A6931. The cell size is represented by(f) in the attached FIG. 1, and it is preferably from 3 to 100 mm,particularly preferably from 5 to 50 mm. The porosity is defined by(volume occupied by the honeycomb body—volume of the partition wallmaterial of the honeycomb body)/volume occupied by the honeycomb body.In the present invention, it is suitably from 92 to 99.5%, particularlyfrom 93 to 98%.

If the porosity of the honeycomb body is smaller than the above range,the foam is likely to deposit on the partition walls of the cells, atthe time of filling, whereby the filling tends to be difficult, and atthe same time, the proportion occupied by the honeycomb body tends to belarge, and the amount of the honeycomb body which readily transmitsheat, increases, whereby the thermal insulation of the honeycomb corematerial deteriorates, and the weight tends to increase, such beingundesirable. On the other hand, if it is large, the proportion occupiedby the honeycomb body tends to be small, and the strength of thehoneycomb core material tends to decrease, such being undesirable. Thethickness of the partition walls of the honeycomb body has an inverselyproportional relation with this porosity, but, it is preferably from0.02 to 3 mm.

The thickness of the honeycomb body is represented by (g) in FIG. 1 andis suitably selected depending upon the required mechanical properties,thermal insulating property, noise insulating property, fire preventingproperty, etc. For example, for partition of an office, a thin thicknessof not more than 50 mm, is preferred, and in a case where fireprevention or flame resistance is required, it is preferably at least 40mm. Further, with a refrigerator-freezer panel which requires a thermalinsulating property, it is preferably from 200 to 400 mm.

The material of the honeycomb body may, for example, be a metal, apaper, a flame retardant paper, a composite material of a fiber and aresin, a plastic, a ceramics or a ceramics paper. The above metal may,for example, be aluminum, stainless steel or steel. The above paper may,for example, be a craft paper, a paper made of a vegetable fiber such aspulp or made of a synthetic fiber such as polyester, polyamide, rayon orpolyvinyl alcohol, a paper made of an organic or inorganic fiber such asaramide paper, graphite paper or glass paper, or a flame retardant paperobtained by adding and mixing magnesium silicate, aluminum hydroxide,antimony oxide, a phosphorus compound, a halogenated compound, a boroncompound, etc. to a fibrous material used therefor during thepreparation of the paper, or by the post impregnation after preparationof the paper or after preparation of a honeycomb.

Further, the composite material of the above fiber and a resin, may, forexample, be a resin-impregnated honeycomb made of a fiber and a resinobtained by impregnating a thermosetting resin such as phenol,polyimide, polyester or epoxy, or a thermoplastic resin such as nylon orpolyimide, to the above-mentioned various papers, and inorganic andorganic woven or non-woven fabrics of e.g. glass, graphite, aramide, athermoplastic polyester, rayon, polyamide, polyvinyl alcohol or pulp.Further, the above plastic honeycomb may, for example, be a honeycombmade of e.g. vinyl chloride, polypropylene, polyethylene, polyurethane,polyimide, polyetherimide or polycarbonate. Further, the above ceramichoneycomb, may, for example, be a honeycomb made of e.g. cordielite ormullite. The above ceramic paper honeycomb, may, for example, be ahoneycomb made of e.g. alumina or alumina silica fiber.

Among them, a metal honeycomb made of aluminum, stainless steel orsteel, a resin-impregnated honeycomb made of a phenol resin-impregnatedhoneycomb or a polyimide resin-impregnated honeycomb, or a flameretardant honeycomb, of which the incineration residue in the teststipulated in JIS-P8128 is at least 40 wt %, is preferred for suchreasons as mechanical properties, heat resistance, flame retardancy,light unit weight and price. It is particularly preferred to employ aflame retardant paper honeycomb having at least 40 wt % of magnesiumsilicate or aluminum hydroxide incorporated, from the viewpoint ofexcellent mechanical strength and thermal insulation property, and a lowprice.

The above aluminum honeycomb is usually one using a foil of an aluminumalloy such as 5052, 5056, 2024, 3003 or 3004 as stipulated in JIS-H4000.The above steel honeycomb is preferably one obtained by bondingrelatively low carbon steel foils with an adhesive, followed byexpanding. Further, the metal honeycomb may be one so-called acorrugated honeycomb obtained by forming a metal foil into a corrugatedshape, followed by bonding, and to such a metal honeycomb, corrosionresistant coating treatment may be applied as the case requires.

When a metal honeycomb is thereby used, the adhesion to the urethanecomponent or the phosphorus-containing acid material in the foam will begood, whereby there will be no slipping off of the foam even with ametal honeycomb having a relatively large cell size, and the handlingefficiency will also be good.

Further, as the phenol resin-impregnated honeycomb and the polyimideresin-impregnated honeycomb, preferred is one having a phenol resin or apolyimide resin impregnated to a paper made of a vegetable fiber such ascraft or pulp, an aramide paper, a glass paper, a glass fiber wovenfabric, a graphite fiber woven fabric or an aramide fiber woven fabric.

It has been found that when a honeycomb containing the above vegetablefiber or an organic substance such as a resin, is used, the honeycombhaving the foam filled in the present invention has a better flameretardation property as a honeycomb core material than the honeycombhaving no foam filled (i.e. the honeycomb itself).

Further, as the flame retardant paper honeycomb containing aluminumhydroxide or magnesium silicate, preferred is one obtained by sheetingaluminum hydroxide or magnesium silicate together with an organic fibersuch as pulp or an inorganic fiber such as a glass fiber into a paperform, and bonding such sheets by an adhesive, followed by expanding.

By using the honeycomb having magnesium silicate or aluminum hydroxideincorporated, the mechanical strength can be remarkably improved overthe mechanical strength of the core material expected from a combinationof a usual honeycomb and a foam.

In the present invention, the filler to be filled in the honeycomb bodyis made of a composite foam comprising an inorganic foam obtained from aphosphorus-containing acid material (a), a curing agent (b) and, ifnecessary, a blowing agent (c), and an organic foam obtained from aurethane prepolymer having NCO groups (d) and water (e). The curingagent (b) and the blowing agent (c) to form the inorganic foam, may be asingle substance having both functions, or may be separate substances,respectively. Such an inorganic foam is excellent in flame retardancyand rigidity, but has a weak point in brittleness. However, with thefoam of the present invention, the brittleness can be substantiallyovercome by the combination with the organic foam obtained from theurethane prepolymer and water.

The ratio of the inorganic foam to the organic foam in the compositefoam relates to the physical property of the filler in the presentinvention, and accordingly relates to the characteristics of thehoneycomb core material. The ratio (by weight) of the inorganic foam/theorganic foam is preferably from 3/1 to 50/1. When the ratio of theinorganic foam to the organic foam is at most 50 times, the adhesivenessand the flexibility are good without brittleness. On the other hand, ifit is at least 3 times, the flame retardation or the fire preventingproperty will be good. Further preferably, this ratio is from 5/1 to30/1.

The composite foam of the present invention can be obtained by filling amixture comprising a phosphorus-containing acid material (a), a curingagent (b), a urethane prepolymer having NCO groups (d), water (e) and,if necessary, a blowing agent (c), in cells of the honeycomb body,followed by foaming and curing, for example, by preparing an aqueousmixture comprising a phosphorus-containing acid material (a), a curingagent (b), a blowing agent (c) and a urethane prepolymer (d), fillingthis mixture in cells of the honeycomb body, and foaming and curing theinorganic foam and the organic foam substantially simultaneously. It isimportant that the inorganic foam made from (a) and (b), and, ifnecessary, (c), and the organic foam made from (d) and (e), aresubstantially simultaneously foamed and cured, and permitted to foam incells of the honeycomb, whereby a composite foam having theabove-mentioned excellent characteristics, can be obtained.

In the composite foam in the present invention, as thephosphorus-containing acid material (a), for example, phosphoric acid,phosphorus acid, phosphoric anhydride, condensed phosphoric acids,polyvalent metal salts of these, salts of a water-soluble amine withsuch polyvalent metal salts, or a mixture of two or more of them, may beused. Among them, it is preferred to use an acid polyvalent metalphosphate such as a polyvalent metal primary phosphate or a polyvalentmetal secondary phosphate, or a salt of such a phosphate with awater-soluble amine, in view of the water resistance, moistureresistance or high cell strength of the foam. As the above polyvalent(bivalent, trivalent or higher valent) metal, magnesium, calcium,aluminum, zinc, barium or iron, may, for example, be mentioned. Amongthem, magnesium, calcium or aluminum is preferred. Instead of a methodof adding in the form of such a polyvalent metal phosphate or apolyvalent metal phosphite, it is possible to employ a method wherein ametal compound chemically active with phosphoric acid or phosphorusacid, for example, a polyvalent metal oxide such as magnesium oxide orcalcium oxide, or a polyvalent metal hydroxide such as aluminumhydroxide, magnesium hydroxide or calcium hydroxide, is added into thesystem separately from the phosphorus-containing acid material such asphosphoric acid or phosphorus acid, and they are reacted in the system.Among them, as the phosphorus-containing acid material (a), it isparticularly preferred to use phosphoric acid, magnesium primaryphosphate, aluminum primary phosphate, zinc primary phosphate or amixture of two or more of them, for such a reason that the waterresistance, moisture resistance or the cell strength of the foam ishigh.

Further, as the phosphorus-containing acid material (a), it is mostpreferred to use a salt of an acid polyvalent metal phosphate with awater-soluble amine. Here, the water-soluble amine means one whichdissolves in water in an amount of at least 1 wt % at 20° C. It isthereby possible to control abrupt foaming and curing of the aqueousmixture thereby to prolong the time in a non-foamed state i.e. the timehaving fluidity, whereby the thickness can be made uniform by e.g.doctor blade, and consequently it can be filled uniformly into therespective cells of the honeycomb body. Further, it is possible to fillthe aqueous mixture into cells of the honeycomb body before it isfoamed, whereby bubbles of the foam will not be damaged by the honeycombbody, and consequently, a constant uniform foaming can be carried out,and it becomes possible to improve the thermal insulating property andto reduce the weight, as the honeycomb core material.

The above water-soluble amine may, for example, be a secondary ortertiary alkyl amine (carbon number: 2 to 18) such as diethylamine,diisopropylamine, diallylamine, triethylamine or triallylamine; aheterocyclic amine (carbon number: 3 to 20) such as pyridine,piperidine, N-methyl piperidine, morpholine, N-methyl morpholine,N-ethyl morpholine or lutidine; an amino alcohol (carbon number: 2 to18) such as monoethanolamine, N,N-dimethylethanolamine or N,N-diethylethanolamine; or a water-soluble amine having a boiling point within arange of from room temperature to about 200° C., such as urea. Preferredas the water-soluble amine is trimethylamine, N-ethyl morpholine,monoethanolamine or urea. The amount of the water-soluble amine to beadded per equivalent of the acid polyvalent metal phosphate is usuallyfrom 0.01 to 1 equivalent, preferably from 0.05 to 0.5 equivalent.

The content of the phosphorus-containing acid material (a) in the foamof the present invention is from 3 to 20 wt %, particularly from 4 to 18wt %, as a preferred range as converted to the atomic amount ofphosphorus in the foam of the present invention. If the content of thephosphorus atom is less than 3 wt %, the flame preventing performance ofthe obtainable foam tends to be low. If the content of the phosphorusatom exceeds 20 wt %, the dispersibility of the prepolymer (d) tends tobe low, whereby it tends to be difficult to obtain a uniform foamedstructure.

As the above curing agent (b) in the foam of the present invention, acarbonate (b1), a metal oxide and/or a metal hydroxide (b2) or a lightmetal (b3) which generates a gas when reacted with an acid or an alkali,may be used, and two or more of them may be used in combination.

As a preferred example of the carbonate (b1), sodium carbonate, sodiumhydrogencarbonate, potassium carbonate, ammonium carbonate, calciumcarbonate, barium carbonate, basic magnesium carbonate or basic zinccarbonate may be mentioned. Among them, a polyvalent metal carbonate ispreferred, and particularly preferred is a basic salt such as basicmagnesium carbonate or basic zinc carbonate.

As a preferred example of the metal oxide (b2), sodium oxide, potassiumoxide, calcium oxide, barium oxide, magnesium oxide or zinc oxide may bementioned. The metal hydroxide (b2) may, for example, be sodiumhydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide,magnesium hydroxide or zinc hydroxide. Among them, a polyvalent metaloxide or a polyvalent metal hydroxide is particularly preferred. As themetal oxide and/or the metal hydroxide (b2), a non-reacted metalcompound used in excess at the time of preparing (a) in a case where asthe phosphorus-containing acid material (a), a reaction product of aphosphorus-containing acid material with a polyvalent metal oxide or apolyvalent metal hydroxide, is used, may be utilized.

As a preferred example of the above light metal (b3), magnesium,aluminum or zinc may be mentioned. Among (b), preferred is (b1) or (b2),and particularly preferred is (b1).

The amount of the above curing agent is preferably from 0.1 to 200 partsby weight, per 100 parts by weight of the phosphorus-containing acidmaterial (a). In the case of the curing agent (b1), it also has afunction as a blowing agent, and it is particularly preferably from 1 to150 parts by weight, when the degree of curing and foaming is taken intoconsideration.

With respect to the blowing agent (c) in the foam of the presentinvention, depending upon the type of the above curing agent (b), noseparate blowing agent is required to be used. Namely, in the case of(b1) and (3), (b1) and (b3) have also a function as a blowing agent (c).Whereas, (b2) has only a function as a curing agent, and it requires ablowing agent (c). As such a blowing agent (c), a low boiling pointorganic solvent, or an organic compound which generates a gas by heatdecomposition, may be mentioned.

The above volatile low boiling point (the boiling point being preferablyat most 120° C.) organic solvent, may, for example, be an ether, aketone, a hydrocarbon or a halogenated hydrocarbon. These blowing agentsmay be used alone or in combination as a mixture of two or more of them.

A preferred example of the above ether is diethyl ether or dipropylether, and a preferred example of the ketone is acetone or methyl ethylketone. A preferred example of the above hydrocarbon is pentane, hexane,heptane, cyclopentane or cyclohexane. A preferred example of the abovehalogenated hydrocarbon is one having a boiling point of from 0 to 100°C., including a chlorinated hydrocarbon such as methylene chloride ortrichloroethylene, a chlorinated fluorohydrocarbon such as2,2-dichloro-1,1,1-trifluoroethane (HCFC123) or1,1-dichloro-1-fluoroethane (HCFC141b), or a fluorinated hydrocarbonsuch as 1,1,1,2,3,3-hexafluoropropane (HFC236ea) or1,1,1,3,3-pentafluoropropane (HFC245fa).

A preferred example of the above-mentioned organic compound whichgenerates a gas by thermal decomposition, is an azo type compound suchas azobisisobutyronitrile, azodicarbonamide or azobisformaldehyde; anitrous compound such as dinitrosopentamethylenetetramine ordinitrosoterephthalamide; a sulfonyl hydrazide compound such asp-toluene sulfonyl hydrazide or P,P′-oxybis(benzene sulfonyl hydrazide);an organic peroxide such as methyl ethyl ketone peroxide, benzoylperoxide or cumene peroxide; or a hydrazo type compound such as hydrazodicarbonamide, isopropyl hydrazo dicarboxylate, tolylhydrazinotriamineor p-toluene sulfonylsemicarbazide. Further, 5-phenyltetrazol, ammoniumcarbonate, ammonium hydrogencarbonate or a compound such as urea, may beused. As the blowing agent (c), a halogenated hydrocarbon having aboiling point of from 0 to 100° C. or acetone may preferably bementioned.

In the present invention, the amount of the blowing agent (c) is usuallyat most 55 parts by weight, preferably from 0.5 to 50 parts by weight,particularly preferably from 5 to 45 parts by weight, per 100 parts byweight of the phosphorus-containing acid material (a). When (b2) is usedas a curing agent, a blowing agent is separately employed. Accordingly,by properly selecting the blowing agent to the curing agent, the foamingtime for the curing reaction can suitably be adjusted, and filling ofthe foam to the honeycomb body will be sufficient. Further, the amountsof the curing agent and the blowing agent may be respectively adjusted,whereby it is easy to adjust the desired hardness within a wide range offrom soft to hard depending upon the foaming ratio.

In the present invention, the urethane prepolymer having NCO groups (d)may be one which is derived from an organic polyisocyanate compound (n)and an active hydrogen-containing compound (h) and which has NCO groupsin its molecule. As such an organic polyisocyanate compound (n), thefollowing (n1) to (n5) may, for example, be mentioned. Here, the carbonnumber in (n1) to (n5) is a value excluding the carbon number in the NCOgroups.

(n1) a C₂₋₁₂ aliphatic polyisocyanate,

(n2) a C₄₋₁₅ alicyclic polyisocyanate,

(n3) a C₈₋₁₂ araliphatic polyisocyanate,

(n4) a C₆₋₂₀ aromatic polyisocyanate,

(n5) a modified product of a polyisocyanate (n1) to (n4).

Specific examples of the aliphatic polyisocyanate (n1) include:

ethylene diisocyanate,

tetramethylene diisocyanate,

hexamethylene diisocyanate (HDI),

dodecamethylene diisocyanate,

2,2,4-trimethylhexamethylene diisocyanate,

lysine diisocyanate, and

1,3,6-hexamethylene triisocyanate.

Specific examples of the alicyclic polyisocyanate (n2) include:

isophorone diisocyanate (IPDI),

dicyclohexylmethane-4-4′-diisocyanate (hydrogenated MDI),

1,4-cyclohexane diisocyanate,

methylcyclohexane-2,4-diisocyanate (hydrogenated TDI), and

1,4-bis(2-isocyanate ethyl)cyclohexane, and the like.

Specific examples of the araliphatic polyisocyanate (n3) include:

p-xylene diisocyanate, and

tetramethylxylene diisocyanate, and the like.

Specific examples of the aromatic polyisocyanate (n4) include:

1,4-phenylene diisocyanate

2,4- or 2,6-toluene diisocyanate (TDI),

diphenylmethane-2,4′- or 4,4′-diisocyanate (MDI),

naphthalene-1,5-diisocyanate,

3,3′-dimethyldiphenylmethane-4,4′-diisocyanate, crude TDI, and

polyphenylmethane polyisocyanate [common name is crude MDI: aphosgenated product of a condensate of an aromatic amine such as anilineor its mixture with formaldehyde (a mixture comprising diaminodiphenylmethane and a small amount, such as from 1 to 20 wt %, of a polyaminehaving at least three amino groups)].

Specific examples of the modified product (n5) of a polyisocyanate (n1)to (n4) include modified products having carbon amide groups, uretidiongroups, uretoimine groups, urea groups, beaulet groups, isocyanurategroups, urethane groups, etc., introduced in place of the isocyanategroups of the polyisocyanates exemplified above as (n1) to (n4).

Selection of such organic polyisocyanate compounds (n) is notparticularly limited, and they may be used alone or in an optionalcombination as a component to produce a polyurethane polymer dependingupon the physical properties of the foam and costs. Among them, HDI,IPDI, hydrogenated MDI, hydrogenated TDI, TDI or MDI is preferred, andparticularly preferred is IPDI, TDI or MDI.

The above active hydrogen-containing compound (h) may, for example, be alow molecular weight polyol (h1) and a high molecular weight polyol(h2). Here, if the range of the molecular weight of each of (h1) and(h2) is represented by the hydroxyl group value, the hydroxyl groupvalue of (h1) is usually from 300 to 1,000 or higher, preferably from350 to 800. Further, the hydroxyl group value of (h2) is usually lessthan 300, preferably from 20 to 250, particularly preferably from 40 to200. Further, the number of functional groups of the activehydrogen-containing compound (h) is usually from 2 to 8 or higher in thecase of either (h1) or (h2).

As the low molecular weight polyol (h1), the following (h1-1) to (h1-6)may be mentioned.

(h1-1) an aliphatic dihydric alcohol

(h1-2) a low molecular weight diol having a cyclic group

(h1-3) a trihydric alcohol

(h1-4) a tetrahydric to octahydric or higher polyhydric alcohol

(h1-5) an alkanolamine

(h1-6) a low mol ethylene oxide and/or propylene oxide adduct of acompound of (h1-1) to (h1-5).

On the other hand, as the high molecular weight polyol (h2), thefollowing (h2-1) to (h2-6) may be mentioned.

(h2-1) a polyoxyalkylene polyol

(h2-2) a polyester polyol

(h2-3) a polyolefin polyol

(h2-4) an acryl polyol

(h2-5) a castor oil polyol

(h2-6) a polymer polyol.

Among the low molecular weight polyols (h1), specific examples of thealiphatic dihydric alcohol (h1-1) include ethylene glycol, diethyleneglycol, propylene glycol, dipropylene glycol, 1,4-butanediol, neopentylglycol, 1,6-hexanediol or 1,8-octamethylenediol, and the like. Specificexamples of the low molecular weight diol (h1-2) having a cyclic groupinclude 1,4-bis(2-hydroxyethoxyphenyl)propane. Specific examples of thetrihydric alcohol (h1-3) include glycerol, trimethylol propane andhexane triol. Specific examples of the tetrafunctional or higherpolyhydric alcohol (h1-4) include sorbitol and sucrose. Specificexamples of the alkanolamine (h1-5) include triethanolamine andmethyldiethanolamine. Specific examples of the above low mol adduct(h1-6) include those having ethylene oxide and/or propylene oxide addedin a low mol within a range such that the hydroxyl value will be atleast 300, to ones mentioned as specific examples of such (h1-1) to(h1-5).

On the other hand, among the high molecular weight polyols (h2), thepolyoxyalkylene polyol (h2-1) may, for example, be one having analkylene oxide added to a compound of (h1-1) to (h1-5) described in theparagraph for the low molecular weight polyol (h1), to a low molecularamine or to a polyhydric phenol. The low molecular amine may, forexample, be a low molecular polyamine such as ethylenediamine,tetramethylenediamine or hexamethylenediamine, or a low molecularmonoamine such as n-butylamine or stearyl amine. The polyhydric phenolmay, for example, be hydroquinone, bisphenol A, bisphenol F or bisphenolS. As the alkylene oxide to be added, a C₂₋₄ alkylene oxide such asethylene oxide, propylene oxide or butylene oxide, or a combinationthereof (in the case of the combination, it may be a block or randomadduct) may, for example, be mentioned. Specific examples of thepolyoxyalkylene polyol (h2-1) include polyoxypropylene glycol,polyoxypropylene triol, polyoxyethylene polyoxypropylene glycol,polyoxyethylene polyoxypropylene triol, polyoxypropylene tetraol andpolyoxytetramethylene glycol.

The polyester polyol (h2-2) may, for example, be the following (h2-21)to (h2-23).

(h2-21) a condensed polyester polyol obtained by reacting a two orhigher functional polyhydric alcohol with a dicarboxylic acid.

(h2-22) a polylactone polyol obtained by ring opening polymerization ofa lactone

(h2-23) a polycarbonate polyol obtained by the reaction of ethylenecarbonate with 1,6-hexanediol.

The dicarboxylic acid which constitutes the condensed polyester polyol(h2-21) may, for example, be a C₂₋₂₀ aliphatic dicarboxylic acid (suchas succinic acid, adipic acid, sebacic acid, glutaric acid, azelaicacid, maleic acid or fumaric acid), a C₈₋₂₄ aromatic dicarboxylic acid(such as terephthalic acid or isophthalic acid), and anhydride, a loweralkyl (carbon number 1 to 4) ester or an acid halide (such as acidchloride) of such a dicarboxylic acid, or a mixture of two or more ofthem. The lactone to be used for the polylactone polyol (h2-22) may, forexample, be ε-caprolactone.

Specific examples of such a polyester polyol (h2-2) include polyethyleneadipate, polybutylene adipate, polyhexamethylene adipate, polyneopentyladipate, polyethylenepolypropylene adipate, polyethylene butyleneadipate, polybutylene hexanemethylene adipate, polydiethylene adipate,poly(polytetramethylenether) adipate, polyethylene azelate, polyethylenesebacate, polybutylene azelate, polybutylene sebacate, polyethyleneterephthalate, polycaprolactone diol and polycarbonate diol.

Specific examples of the polyolefin polyol (h2-3) include polybutadienepolyol, hydrogenated polybutadiene polyol and polyisoprene polyol.Specific examples of the acryl polyol (h2-4) include a copolymer ofhydroxyethyl acrylate with ethyl acrylate, and a copolymer ofhydroxyethyl acrylate, ethyl acrylate and styrene. The castor oil typepolyol (h2-5) may, for example, be (h2-51) castor oil; (h2-52) apolyester polyol of a castor oil fatty acid with a polyhydric alcohol ora polyoxyalkylene polyol; or a mixture of two or more of them. Specificexamples of (h2-52) include a mono-, di- or tri-ester of a castor oilfatty acid with trimethylolpropane; and a mono- or di-ester of a castoroil fatty acid with polyoxypropylene glycol.

The polymer polyol (h2-6) may, for example, be one obtainable bypolymerizing an ethylenically unsaturated monomer disclosed in U.S. Pat.No. 3,383,351 such as acrylonitrile or styrene among high molecularweight polyols exemplified as (h2-1) to (h2-5). The content of theethylenically unsaturated monomer unit constituting the polymer polyol(h2-6) is usually from 0.1 to 70 wt %, preferably from 5.0 to 60 wt %.As a method for producing the polymer polyol (h2-6), a method ofpolymerizing the ethylenically unsaturated monomer in a polyol in thepresence of a polymerization initiator (such as a radical-generatingagent) (such as the method disclosed in U.S. Pat. No. 3,383,351) may,for example, be mentioned.

Among those exemplified in the foregoing as the activehydrogen-containing compound (h), particularly preferred is an ethyleneoxide adduct among polyoxyalkylene polyols (h2-1), and it is preferredto use the ethylene oxide adduct alone or as a part of the activehydrogen-containing compound (h). In such a case, the content of theoxyethylene units in the active hydrogen-containing compound (h) ispreferably from 10 to 95 wt %, particularly preferably from 50 to 90 wt%. By using such an ethylene oxide adduct, the dispersibility of theprepolymer (d) at the time of preparing the aqueous mixture, will beimproved.

The low molecular weight polyol (h1) and the high molecular weightpolyol (h2) may be used alone, respectively, or may be used incombination, and the ratio of the low molecular weight polyol (h1) tothe high molecular weight polyol (h2) is not particularly limited. Forexample, in order to improve the effect for overcoming the brittlenessof the foam or in order to increase the effect for imparting theflexibility, the ratio of (h2) is preferably increased so that theweight ratio of (h1):(h2)=(0 to 50):(50 to 100). On the other hand, inorder to increase the rigidity of the foam, the ratio of (h1) ispreferably increased so that the weight ratio of (h1):(h2)=(50 to100):(0 to 50).

Further, in order to adjust the molecular weight or viscosity of theprepolymer (d), a monool (h3) may be incorporated as component (h), asthe case requires. The monool (h3) may, for example, be an aliphaticmonohydric alcohol such as methanol, ethanol, isopropanol, butanol,pentanol, 2-ethylhexanol or dodecanol, or an alkylene oxide (such asethylene oxide or propylene oxide) adduct of an alkylphenol (such asoctyl phenol, nonyl phenol or dodecyl phenol). The hydroxyl value of themonool (h3) is usually within the same range as (h1) or (h2). Theproportion of the monool (h3) to be used as the case requires, in theactive hydrogen compound (h), is usually within a range wherein theaverage number of functional groups of (h) will be at least 2,preferably at least 2.5.

The NCO content in the above urethane prepolymer (d) is preferably from0.5 to 30 wt %. Further, the nature of the urethane prepolymer (d) ispreferably liquid at room temperature, and preferably has a molecularweight and a molecular composition of certain degrees. Its numberaverage molecular weight by gel permeation chromatography is preferablyfrom 1,000 to 50,000.

The urethane prepolymer (d) can be produced by charging the organicpolyisocyanate and the active hydrogen-containing compound in a reactorand reacting them at a temperature of from 50 to 120° C. The content ofthe urethane prepolymer (d) units in the foam in the present invention,i.e. the content of (d) to the total solid content at the time of thepreparation of the foam is preferably from 3 to 30 wt %, particularlypreferably from 5 to 25 wt %. To the foam of the present invention,boric acid or a polyvalent metal borate may be incorporated in an amountof from 1 to 50 wt % in the foam in order to maintain the shape afterincineration or in order to suppress heat generation or smokegeneration.

To the foam of the present invention, an inorganic filler may beincorporated as the case requires, taking the physical properties andthe cost into consideration. The inorganic filler may, for example, be acement (such as portland cement or alumina cement), a clay mineral (suchas monmorillonite or bentonite), an inorganic light weight aggregate(such as perlite or silas balloon), an inorganic fiber (such as rockwool or glass wool), fly ash, silica fume, silica powder, ceramicpowder, aluminum hydroxide, alumina, calcium sulfate, or otherwater-insoluble inorganic powder material. Further, an organic fiber mayalso be incorporated in order to improve the tensile strength, thebending strength, etc., of the foam. The amount of such a material isnot particularly limited, and it is usually at most 1,800 parts byweight, preferably from 10 to 500 parts by weight per 100 parts byweight of the phosphorus-containing acid material (a).

The foam of the present invention may be foamed and cured by an additionof a flame retardant in order to impart a still higher fire preventingproperty. Preferred examples of the flame retardant include anon-halogen phosphoric acid ester, a halogen-containing phosphoric acidester, an active hydrogen-containing flame retardant, antimony trioxide,antimony pentoxide, and zinc oxide. These may be used in combination asa mixture of two or more of them. The amount of the flame retardant ispreferably at most 40 parts by weight, particularly preferably from 0.1to 30 parts by weight, per 100 parts by weight of the urethaneprepolymer.

According to the present invention, the phosphorus-containing acidmaterial (a), the curing agent (b), the prepolymer (d), water (e) and,if necessary, the blowing agent (c), are mixed to obtain an aqueousmixture, which is filled in cells of a honeycomb, followed by foamingand curing to obtain the honeycomb core material of the presentinvention. The amount of water in the aqueous mixture may be within arange where slurring is possible, and it is not necessary to add watermore than necessary. If the water is large, it takes time and labor todry the foamed and cured product. The amount of water is preferably suchthat the concentration of the solid content in the mixture will be from50 to 90 wt %.

In the present invention, a catalyst may, for example, be used in orderto control the curing speed of the prepolymer (d) to form the organicfoam. Preferred examples of such a catalyst include a metal typecatalyst such as dibutyltin dilaurate, an alkyl titanate, an organicsilicon titanate, stanous octoate, lead octylate, zinc octylate, bismuthoctylate, dibutyltin diorthophenylphenoxite, a reaction product of tinoxide with an ester compound (such as dioctyl phthalate), and an aminetype catalyst such as a monoamine (such as triethylamine), a diamine(such as N,N,N′,N′-tetramethylethylenediamine), a triamine (such asN,N,N′,N″,N″-pentamethyldiethylenetriamine), or a cyclic amine (such astriethylenediamine). The amount of the catalyst is usually at most 7parts by weight, preferably from 0.001 to 5 parts by weight, per 100parts by weight of the prepolymer (d).

Further, in the present invention, a foam stabilizer may be employed inorder to control the cell structure of the foam to be formed. As apreferred example of such a foam stabilizer, the silicon type surfactantmay be mentioned. For example, “SH-192”, “SH-193” or “SH-194”,manufactured by Dow Corning Toray Silicon Co., Ltd., “TFA-4200”,manufactured by Toshiba Silicons, “L-5320”, “L-5340” or “L-5350”,manufactured by Nippon Unicar Company Limited, and “F-121” or “F-122”,manufactured by Shin-Etsu Chemical Co., Ltd., may be mentioned. Theamount of the foam stabilizer is usually at most 2 parts by weight,preferably from 0.001 to 1 part by weight, per 100 parts by weight ofthe urethane prepolymer.

In the present invention, a preferred specific method of preparing theabove aqueous mixture and foaming and curing it in cells of a honeycomb,is as follows. The aqueous mixture may be prepared by mixing thephosphorus-containing acid material (a), the curing agent (b), theprepolymer (d), water (e) and the blowing agent (c) which is used as thecase requires, and the inorganic filler all at once. Otherwise, it maybe prepared by mixing the phosphorus-containing acid material (a) or itsaqueous solution and the prepolymer (d) and then mixing the curing agent(b), and the blowing agent (c) which may be used as the case requires,and the inorganic filler, separately, or preliminarily mixing them toform a slurry, which is then mixed.

A method of filling the above aqueous mixture in cells of a honeycombbody, is not particularly limited, and a method of introducing aslurry-form aqueous mixture into cells, a filling method by spraying, ora method of smoothing the aqueous mixture in a flat shape, and thenpressing a honeycomb body from above to fill it, may, for example, bementioned. In such a method, it is preferred that after filling theaqueous mixture in the honeycomb body, a flat smooth face member is puton the filled honeycomb body face to sufficiently fix it, whereby it ispossible to prevent swelling of the foam out of the cells of thehoneycomb body. Further, the aqueous mixture may not necessarily befilled in all cells of the honeycomb body or in entire cells. Thus, itis possible to produce a honeycomb core material having the foam filledin a part of cells along the thickness direction of the honeycomb body.The filling ratio of the above aqueous mixture in cells of the honeycombbody is usually at least 20 vol %, preferably from 30 to 100 vol %.

The above aqueous mixture is filled in cells of the honeycomb body andthen preferably foamed for a few second to a few tens minutes underordinary temperature and ordinary pressure conditions, and then curingis completed to form a foam. However, in a case where the temperature islow during the winter, or in a case where it is desired to shorten thefoaming and curing time from the viewpoint of the process, it may beheated to a level of 50° C. while being left to stand still. Thereafter,it may be heated to a temperature of from 80 to 100° C., as the caserequires, to remove excess water.

The inorganic and organic composite foam of the present invention thusproduced, has excellent characteristics as described above. Particularlyby controlling the amounts of the polyvalent metal carbonate (b1), thelight metal (b3) and the blowing agent (c) contained in the aboveaqueous mixture, its specific gravity can be adjusted within a widerange of from 0.01 to 1.5. Especially, with the composite foam of thepresent invention, if the specific gravity is low at a level of 0.1 orlower, the flexibility of the foam will be intensely developed, andconsequently, the obtainable honeycomb core material will haveflexibility.

Thus, in the present invention, it is possible to obtain a honeycombcore material having a composite foam of a wide range of materialranging from a hard material to a soft material. Further, in the presentinvention, the thermal insulating performance of the obtained honeycombcore material may be adjusted by selecting the material of the honeycombbody and controlling the composition of the above aqueous mixture,particularly by controlling the specific gravity, for example, to imparta low thermal conductivity of a level of at most 0.04 kcal/m·hr·° C.,and the fire preventing property is also corresponding to the level ofnon-combustible to semi-non-combustible material.

As the surface materials to be bonded to the honeycomb core material inthe present invention, metal plates may, for example, be steel plates,aluminum alloy plates, stainless steel plates or titanium alloy plates;wood plates may, for example, be plywood plates, particle boards, MDF(medium fiber plates), lauan or cryptomeria boards; and plastic platesmay be FRP plates, vinyl chloride plates, acrylic plates, or foams ofrelatively hardly inflammable resin such as polyurethane, polystyrene,polyethylene, phenol, melamine or urea resin. Further, inorganic platesmay, for example, be gypsum plates, slate plates, calcium silicateplates, tiles or ceramic plates; and natural stone plates may, forexample, be marble, granite, limestone or travertine. Further, to suchsurface materials, one or more treatments such as coating, plating,lining with a facing material, resin dressing or coating, primertreatment, rust preventive treatment, antibacterial treatment, andantifungal treatment, may be applied, as the case requires.

From the viewpoint of the fire resistance, flame retardancy, strengthand ornamental appearance, the above steel plates, may, for example, becolored steel plates, galvanium steel plates, bonde steel plates or zingplated steel plates. The above aluminum alloy plates may, for example,be Al—Mg type alloy 5000 type of non-heat treated alloy (corrosionresistant aluminum alloy), Al,Cu,Mg type alloy 2000 type of heat-treatedalloy (high power aluminum alloy), Al,Mg,Si type alloy 6000 type, orAl,Zn,Mg type alloy 7000 type. The stainless steel plates may, forexample, be SUS430, or SUS 304. These metal plates and titanium alloyplates are preferably employed. Further, the above-mentioned inorganicplates and natural stone plates are suitable. Further, as the plasticplates, those obtained by foaming a relatively hardly inflammable resinsuch as the above-mentioned phenol, melamine or urea resin, aresuitable, and flame retardant boards having them reinforced with aninorganic fiber, are preferred.

Further, in the case of bonding the surface materials to the honeycombcore material, an adhesive or a solder may be employed, or a method suchas diffusion bonding, may be employed. Among them, a method of using anadhesive is common. The adhesive may, for example, be a thermosettingtype adhesive such as an epoxy type, urethane type or vinyl phenolictype, or a thermoplastic adhesive such as a synthetic rubber type orvinyl acetate type. Its formulation may be in the form of a solution, apaste, a solid or a film. Such an adhesive is selected suitablydepending upon the material of the surface materials and the honeycombbody, the adhesive strength, the curing conditions, the bondinginstallation, the durability, the cost, etc. Further, the bonding methodmay, for example, be a turn back method, a pinch roller method, a hotpress method, a vacuum back method or an autoclave method. These methodsmay be employed alone or in combination. Further, to the bonding surfaceof the surface materials to be bonded, primer treatment or degreasingtreatment, and treatment to roughen the bonding surface such as sanding,may be applied depending upon the adhesive.

Now, the present invention will be described in further detail withreference to Examples. However, it should be understood that theinterpretation of the present invention is by no means restricted bysuch Examples.

EXAMPLE 1

A 50 wt % aqueous solution of magnesium primary phosphate (a-1) put in atank A, a TDI prepolymer (d-1) put in a tank D flashed with nitrogen toavoid a reaction with moisture in air, and basic magnesium carbonate(b-1) put in a tank B, were prepared. From the above respective tanks,firstly, (a-1) and (d-1) were withdrawn so that (a-1)/(d-1) would be 50parts by weight/5 parts by weight, and mixed and stirred by a spiral pinmixer. Immediately thereafter, (b-1) was added in an amount of 30 partsby weight by a vibration feeder, followed by further mixing.

The TDI prepolymer (d-1) used in this Example 1 and in the followingExamples, represents the following. To 100 parts by weight of TDI-80[Colonate T-80, tradename, manufactured by Nippon Polyurethane IndustryCo., Ltd.], 420 parts by weight of polyoxyethylene polyoxypropyleneglycol [molecular weight: 2188, a block copolymer comprising 60 wt % ofethylene oxide and 40 wt % of propylene oxide] was reacted to obtain theprepolymer. The prepolymer had a NCO content of 6.2 wt % and a numberaverage molecular weight of 1,355 and was a viscous resin solution atroom temperature.

The obtained slurry-form aqueous mixture was discharged on a PET(polyethylene terephthalate) film from a discharge outlet of the spiralpin mixer (manufactured by Pacific Machinery & Engineering Co., Ltd.) sothat the thickness would be flat and smooth, and transferred onto a beltpress. The coated amount at that time was 1.50 kg/m².

Further, a separately prepared flame retardant paper honeycomb bodyhaving a cell size of 17 mm, a porosity of 95.3% and a thickness of 40mm and containing magnesium silicate in an amount of 77 wt % of thetotal weight, was placed above the aqueous mixture and retained for 3minutes in a state pressed by a belt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 80% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 2.0 kg/m².

EXAMPLE 2

In the same manner as in Example 1, a 50 wt % aqueous solution ofmagnesium primary phosphate (a-1) put in a tank A, and a TDI prepolymer(d-1) put in a tank D flashed with nitrogen to avoid a reaction withmoisture in air, were prepared, and magnesium oxide (b-2) put in a tankB, and acetone (c-1) put in a tank C, were prepared. From the aboverespective tanks, firstly, (a-1) and (d-1) were withdrawn so that(a-1)/(d-1) would be 50 parts by weight/5 parts by weight, and mixed andstirred by a spiral pin mixer. Immediately thereafter, 10 parts byweight of (c-1) and 40 parts by weight of (b-2) were added by avibration feeder, followed by further mixing.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer so that the thicknesswould be flat and smooth, and transferred onto a belt press. The coatedamount at that time was 1.68 kg/m².

Further, a separately prepared paper honeycomb body which was the sameas in Example 1, was placed from above the aqueous mixture and retainedfor 3 minutes in a state pressed by a belt press. During the retentionby the belt press, foaming and curing of the above aqueous mixturecompleted, and the formed foam occupied about 70% of the thickness ofthe honeycomb. Thereafter, excess water was evaporated by heating anddrying at 90° C. for two hours. The weight of the obtained honeycombcore material was 2.1 kg/m².

EXAMPLE 3

In the same manner as in Example 1, a TDI prepolymer (d-1) put in a tankD flashed with nitrogen to avoid a reaction with moisture in air, andbasic magnesium carbonate (b-1) put in a tank B, were prepared, exceptthat a salt (a-2) prepared by mixing a 50 wt % aqueous solution ofmagnesium primary phosphate and triethylamine in a weight ratio of 19:1and put in a tank A, was prepared. From the above respective tanks,firstly, (a-2) and (d-1) were withdrawn so that (a-2)/(d-1) would be 53parts by weight/5 parts by weight, and mixed and stirred by a spiral pinmixer. Immediately thereafter, (b-1) was added in an amount of 30 partsby weight, by a vibration feeder, followed by further mixing.

The obtained slurry-form aqueous mixture was discharged on a PET(polyethylene terephthalate) film from a discharge outlet of the spiralpin mixer, and after making the thickness sufficiently uniform by meansof a doctor blade, transferred onto a belt press. The coated amount atthat time was 1.55 kg/m².

Further, a separately prepared paper honeycomb body which was the sameas in Example 1, was placed from above the aqueous mixture and retainedfor 3 minutes in a state pressed by a belt press. During the retentionby the belt press, foaming and curing of the above aqueous mixturecompleted, and the formed foam was uniform in the amount filled in eachhoneycomb cell and occupied about 70% of the thickness of the honeycomb.With this honeycomb core material, the foaming speed was lowered, sothat the above aqueous mixture was maintained in a non-foamed state i.e.the time having fluidity was prolonged, whereby it was possible to makethe thickness sufficiently uniform, and as a result, the amount filledin each honeycomb cell was uniform. Thereafter, excess water wasevaporated by heating and drying at 90° C. for two hours. The weight ofthe obtained honeycomb core material was 2.0 kg/m².

EXAMPLE 4

Filling in the honeycomb body was carried out in the same manner exceptthat the triethylamine in Example 3 was changed to urea, and a 50 wt %aqueous solution of magnesium primary phosphate and urea were mixed in aweight ratio of 99:1. The formed foam was uniform in the amount filledin each honeycomb cell and occupied about 70% of the thickness of thehoneycomb. With this honeycomb core material, the foaming speed waslowered, so that the above aqueous mixture was maintained in anon-foamed state i.e. the time having fluidity was prolonged, whereby itwas possible to make the thickness sufficiently uniform, and as aresult, the amount filled in each honeycomb cell was uniform.Thereafter, excess water was evaporated by heating and drying at 90° C.for two hours. The weight of the obtained honeycomb core material was2.1 kg/m².

EXAMPLE 5

Between a semicylindrical convex die having a diameter of 600 mm and ahalf pipe-form concave die having a diameter of 640 mm, a color steelplate having a thickness of 0.5 mm and having a two-component roomtemperature curable epoxy type adhesive coated on one side for ahoneycomb core material, was placed, and the honeycomb core materialprepared in Example 1 was placed thereon. Further, a color steel platehaving a two-pack room temperature curable epoxy type adhesive coated onone side in the same manner was placed thereon, whereupon the dies wereclosed and left to stand at room temperature for 24 hours to let theadhesive cure, thereby to obtain a sandwich panel having a curvedsurface. At that time, the honeycomb core material was free fromcracking or free from falling off from the foam, and its adhesion to thesteel plates was perfect.

EXAMPLE 6

In the same manner as in Example 3, a salt (a-2) prepared by mixing a 50wt % aqueous solution of magnesium primary phosphate and triethylaminein a weight ratio of 19:1 and put in a tank A, a TDI prepolymer (d-1)put in a tank D flashed with nitrogen to avoid a reaction with moisturein air, and basic magnesium carbonate (b-1) put in a tank B, wereprepared. From the above respective tanks, firstly, (a-2) and (d-1) werewithdrawn so that (a-2)/(d-1) would be 53 parts by weight/5 parts byweight, and mixed and stirred by a spiral pin mixer. Immediatelythereafter, (b-1) was added in an amount of 30 parts by weight by avibration feeder, followed by further mixing.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer, so that the thicknesswould be smooth and flat and transferred onto a belt press. The coatedamount at that time was 1.52 kg/m².

Further, a separately prepared a flame retardant paper honeycomb bodyhaving a cell size of 19 mm, a porosity of 96.0% and thickness of 40 mmand containing aluminum hydroxide in an amount of 47 wt % of the totalweight and rock wool in an amount of 24 wt %, was placed from above theaqueous mixture and retained for 3 minutes in a state pressed by thebelt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 90% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 2.2 kg/m².

EXAMPLE 7

In the same manner as in Example 3, a salt (a-2) prepared by mixing a 50wt % aqueous solution of magnesium primary phosphate and triethylaminein a weight ratio of 19:1 and put in a tank A, a TDI prepolymer (d-1)put in a tank D flashed with nitrogen to avoid a reaction with moisturein air, and basic magnesium carbonate (b-1) put in a tank B, wereprepared. From the above respective tanks, firstly, (a-2) and (d-1) werewithdrawn so that (a-2)/(d-1) would be 53 parts by weight/S parts byweight, and mixed and stirred by a spiral pin mixer. Immediatelythereafter, (b-1) was added in an amount of 30 parts by weight by avibration feeder, followed by further mixing.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer, so that the thicknesswould be smooth and flat and transferred onto a belt press. The coatedamount at that time was 1.52 kg/².

Further, a separately prepared a craft paper honeycomb body having acell size of 19 mm, a porosity of 95.8% and a thickness of 40 mm, wasplaced from above the aqueous mixture and retained for 3 minutes in astate pressed by the belt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 90% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 2.1 kg /m².

EXAMPLE 8

In the same manner as in Example 3, a salt (a-2) prepared by mixing a 50wt % aqueous solution of magnesium primary phosphate and triethylaminein a weight ratio of 19:1 and put in a tank A, a TDI prepolymer (d-1)put in a tank D flashed with nitrogen to avoid a reaction with moisturein air, and basic magnesium carbonate (b-1) put in a tank B, wereprepared. From the above respective tanks, firstly, (a-2) and (d-1) werewithdrawn so that (a-2)/(d-1) would be 53 parts by weight/5 parts byweight, and mixed and stirred by a spiral pin mixer. Immediatelythereafter, (b-1) was added in an amount of 30 parts by weight by avibration feeder, followed by further mixing.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer, so that the thicknesswould be smooth and flat and transferred onto a belt press. The coatedamount at that time was 1.50 kg/m².

Further, a separately prepared aluminum honeycomb body having a cellsize of 9.5 mm, a porosity of 98.2% and a thickness of 40 mm, was placedfrom above the aqueous mixture, and retained for 3 minutes in a statepressed by the belt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 90% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 2.4 kg/m².

COMPARATIVE EXAMPLE 1

A 50 wt % aqueous solution of magnesium primary phosphate (a-1) put in atank A and basic magnesium carbonate (b-1) put in a tank B, wereprepared. 30 Parts by weight of (b-1) was added to 50 parts by weight of(a-1), from the respective tanks, followed by mixing by a spiral pinmixer.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer, so that the thicknesswould be smooth and flat, and transferred onto a belt press. The coatedamount at that time was 1.50 kg/m².

Further, a separately prepared paper honeycomb body which was the sameas in Example 1, was put from above the aqueous mixture and retained for3 minutes in a state pressed by the belt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 50% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 2.2 kg/m².

COMPARATIVE EXAMPLE 2

A 50 wt % aqueous solution of magnesium primary phosphate (a-1) put in atank A, magnesium oxide (d-2) put in a tank B, and acetone (c-1) put ina tank C, were prepared. 10 Parts by weight of (c-1) and 40 parts byweight of (b-2) were added to 50 parts by weight of (a-1), from theabove respective tanks, followed by mixing by a spiral pin mixer.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer, so that the thicknesswould be smooth and flat and transferred onto a belt press. The coatedamount at that time was 1.53 kg/r².

Further, a separately prepared a paper honeycomb body which was the sameas in Example 1, was put from above the aqueous mixture, and retainedfor 3 minutes in a state pressed by the belt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 40% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 2.2 kg/m².

COMPARATIVE EXAMPLE 3

In the same manner as in Example 1, a 50 wt % aqueous solution ofmagnesium primary phosphate (a-1) put in a tank A, a TDI prepolymer(d-1) put in a tank D flashed with nitrogen to avoid a reaction withmoisture in air, and basic magnesium carbonate (d-1) put in a tank D,were prepared. From the above respective tanks, firstly, (a-1) and (d-1)were withdrawn so that (a-1)/(d-1) would be 50 parts by weight/5 partsby weight, and mixed and stirred by a spiral pin mixer. Immediatelythereafter, (b-1) was added in an amount of 30 parts by weight by avibration feeder, followed by further mixing.

The obtained slurry-form aqueous mixture was discharged on a PET filmfrom a discharge outlet of the spiral pin mixer, so that the thicknesswould be smooth and flat and transferred onto a belt press. The coatedamount at that time was 1.50 kg/m².

Further, cells of a paper honeycomb body having a cell size of 16 mm, aporosity of 95.3% and thickness of 40 mm and containing 77 wt % ofmagnesium silicate, were partially cut off to prepare a honeycomb bodyhaving a cell size of 120 mm and a porosity of 98.3%. Such a honeycombbody was placed from above the aqueous mixture, and retained for 3minutes in a state pressed by the belt press.

During the retention by the belt press, foaming and curing of the aboveaqueous mixture completed, and the formed foam occupied about 80% of thethickness of the honeycomb. Thereafter, excess water was evaporated byheating and drying at 90° C. for two hours. The weight of the obtainedhoneycomb core material was 1.4 kg/m².

COMPARATIVE EXAMPLE 4

Parts by weight of a novolac type solid phenol resin, 10 parts by weightof hexamethylenetetramine and 5 parts by weight ofdinitrosopentamethylenetetramine were kneaded by a metal roll, followedby pulverization to obtain a powder material for a foam, of from 50 to150 mesh. Such a powder material was applied on a PET film in a size of60 cm×90 cm in an amount of 1.2 kg/m², and sandwiched with another PETfilm, followed by heat pressing at 120° C. for 5 minutes and then bycooling to room temperature. The powder material was once plasticized byheating, and became a plate state when further cooled.

Further, a separately prepared paper honeycomb body which was the sameas in Example 1, was placed from above a plate-form material having aPET film on one side peeled, followed by heat pressing at 160° C. for 60minutes and then by cooling to room temperature. The formed phenol foamoccupied about 80% of the thickness of the honeycomb. The weight of theobtained honeycomb core material was 2.3 kg/m².

COMPARATIVE EXAMPLE 5

In the same manner as in Example 5, between a semicylindrical convex diehaving a diameter of 600 mm and a half pipe-form concave die having adiameter of 640 mm, a color steel plate having a thickness of 0.5 mm andhaving a two-pack room temperature curable epoxy type adhesive coated onone side for a honeycomb core material, was placed, and the honeycombcore material prepared in Comparative Example 1 was placed thereon.Further, a color steel plate having a two-pack room temperature curableepoxy type adhesive coated on one side in the same manner was placedthereon, whereupon the dies were closed and left to stand at roomtemperature for 24 hours to let the adhesive cure thereby to obtain asandwich panel having a curved surface.

The foam peeled from the honeycomb partition walls, and further,cracking of the honeycomb was observed on the concave side of thehoneycomb core material. Further, on the convex side, the foam broken bywarping of the honeycomb core material was sandwiched between thehoneycomb and the steel plate, and peeling of the steel plate wasobserved.

COMPARATIVE EXAMPLE 6

The same magnesium silicate-containing paper honeycomb as used inExamples 1 to 4 and in Comparative Examples 1, 2 and 4, was used byitself as a core material.

COMPARATIVE EXAMPLE 7

The same aluminum hydroxide-containing paper honeycomb as used inExample 6, was used by itself as a core material.

COMPARATIVE EXAMPLE 8

The same craft paper honeycomb as used in Example 7, was used by itselfas a core material.

With respect to the honeycomb core materials obtained in the aboveExamples and Comparative Examples (excluding Example 5 and ComparativeExample 5), (1) flexibility of the honeycomb core material, (2) slippingoff of the filler of the honeycomb core material, (3) the thermalconductivity of the honeycomb core material, (4) the non-flammability ofthe honeycomb core material, and (5) the compression strength of thesandwich panel, were tested. The results are shown in the attachedTables 1 and 2. The test methods for the above items are as follows.

(1) Flexibility of the Honeycomb Core Material

The honeycomb core material was cut into a size of 600×300 (providedthat the longitudinal direction was the expansion direction of thehoneycomb body) and supported at two points with a span of 500 mm(provided that the aqueous mixture coated side during the preparationfaced downwardly), whereby the deflection at the center portion wasmeasured.

(2) Slipping off of the Filler of the Honeycomb Core Material

The above test table supported at two points was vibrated at a vibrationamplitude of 10 mm at 100 Hz for 3 minutes, whereupon slipping off anddisplacement of the filler was visually evaluated.

(3) Thermal Conductivity of the Honeycomb Core Material

Measured by JIS A1412.

(4) Non-flammability of the Honeycomb Core Material

The maximum ultimate temperature in the Non-combustibility teststipulated in Notice No. 1828 by Ministry of Construction, Japan, in1970.

(5) Compression Strength of the Sandwich Panel

The sandwich panel having color steel plates of 0.8 mm bonded on bothsides of the honeycomb core material by an epoxy type adhesive, wasmeasured in accordance with JIS K9511.

INDUSTRIAL APPLICABILITY

The honeycomb core material according to the present invention isexcellent in flame retardation and non-flammability, which can not beattained by a conventional organic foam, and is flexible and haselasticity, which can not be obtained by a conventional inorganic foam,since the filler in its cells is the above-mentioned inorganic andorganic composite foam.

In addition, it has an extremely high adhesion between the honeycomb andthe filler, whereby it is free from slipping off of the filler from thehoneycomb body, and transportation and handling are easy.

Further, the foam has flexibility, and modification after thepreparation is possible, whereby attachment of a flat surface materialis good, and a honeycomb core material suitable also for a structurehaving a curved surface, can be provided.

Further, a method for producing a honeycomb core material is provided,wherein in cells of a honeycomb body, a aqueous mixture comprising aphosphorus-containing acid material, a curing agent, a blowing agent anda urethane polymer having NCO groups, is foamed and cured substantiallysimultaneously to form the above-mentioned composite foam comprising aninorganic foam and an organic foam.

Further, a method for producing a honeycomb core material is alsoprovided wherein foaming and curing are suppressed before filling of theabove aqueous mixture into cells of the honeycomb body, and thecomposite foam is uniformly formed in the cells of the honeycomb body.

TABLE 1 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 6 Ex. 7 Ex. 8 Flexibility of thehoneycomb 32 25 20 21 35 33 10 core material (mm) Slipping off of thehoneycomb ∘ ∘ ∘ ∘ ∘ ∘ ∘ core material Thermal conductivity of the 0.0340.036 0.038 0.038 0.035 0.040 0.052 honeycomb core material (kcal/ mh°C.) Non-flammability of the honey- 778 784 780 781 796 820 770 comb corematerial (° C.) Compression strength (kgf/cm²) 3.2 3.1 3.2 3.1 3.4 4.615.2

TABLE 2 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 1 Ex. 2 Ex. 3 Ex.4 Ex. 6 Ex. 7 Ex. 8 Flexibility of the honeycomb 3 5 55 3 90 95 80 corematerial (mm) Slipping off of the honeycomb x x ∘ x — — — core materialThermal conductivity of the 0.052 0.055 0.033 0.040 — — — honeycomb corematerial (kcal/ mh° C.) Non-flammability of the honey- 780 782 775 851795 823 890 comb core material (° C.) Compression strength (kgf/cm²) 3.23.1 0.2 3.1 1.6 1.8 4.5

What is claimed is:
 1. A honeycomb core material for a sandwichstructure, which comprises a honeycomb body and a filler filled in atleast a part of cells thereof, wherein the honeycomb body has a cellsize of from 5 to 50 mm and a porosity of from 92 to 99.5%, asstipulated in JIS-A6931, and the honeycomb body is a resin-impregnatedpaper honeycomb or a flame-retardant paper honeycomb, of which anincineration residue in the test stipulated in JIS-P8128 is at least40%, wherein the filler is a composite foam comprising an inorganic foamobtained from a phosphorus-containing acid material (a), a curing agent(b) and, optionally, a blowing agent (c), and an organic foam obtainedfrom a urethane prepolymer having NCO groups (d), and water (e), andwherein the material has a flexibility of from 10 mm to 35 mm asmeasured by the deflection at the centerpoint of a 500 mm span of a600×300 mm section of the material having a thickness of 40 mm.
 2. Thematerial according to claim 1, comprising a flame-retardant paperhoneycomb comprising magnesium silicate or aluminum hydroxide in anamount of at least 40 wt %.
 3. The material according to claim 1,wherein the phosphorus-containing acid material (a) is at least onemember selected from the group consisting of phosphoric acid, phosphorusacid, phosphoric anhydride, condensed phosphoric acids, polyvalent metalsalts thereof, and salts of a water-soluble amine with a polyvalentmetal salt.
 4. The material according to claim 1, wherein thephosphorus-containing acid material (a) is a salt of an acid polyvalentmetal phosphate with a water-soluble amine.
 5. The material according toclaim 1, wherein the curing agent (b) is at least one member selectedfrom the group consisting of a carbonate (b1), a metal oxide and/or ametal hydroxide (b2), and a light metal (b3) which generates a gas whenreacted with an acid or an alkali.
 6. The material according to claim 1,wherein the curing agent (b) is at least one of a metal oxide or a metalhydroxide (b2), and the blowing agent (c) is at least one of a lowboiling point organic solvent or an organic compound which generates agas by thermal decomposition.
 7. A method comprising, filling a mixturecomprising a phosphorus-containing acid material (a), a curing agent(b), a urethane prepolymer having NCO groups (d), water (e) and,optionally, a blowing agent (c), in cells of a paper honeycomb bodyhaving a cell size of from 5 to 50 mm and a porosity of from 92 to99.5%, as stipulated in JIS-A6931, followed by foaming and curing, toproduce a honeycomb core material having a flexibility of from 10 mm to35 mm as measured by the deflection at the centerpoint of a 500 mm spanof a 600×300 mm section of the material having a thickness of 40 mm. 8.A sandwich structure which comprises the material of claim 1, and one ormore surface materials bonded to both sides of the material.
 9. Thematerial of claim 1, wherein the phosphorus-containing acid material isa magnesium primary phosphate, the curing agent is basic magnesiumcarbonate.
 10. The material of claim 1, wherein the weight ratio of theinorganic foam to the organic foam is from 3:1 to 50:1.
 11. The materialof claim 1, wherein the phosphorus-containing acid material (a) ispresent in an amount of from 3 to 20 wt % in the inorganic foam.
 12. Aflexible material which comprises a honeycomb body and a filler filledin at least a part of cells thereof, wherein the honeycomb body has acell size of from 3 to 100 mm and a porosity of from 92 to 99.5%, asstipulated in JIS-A6931, wherein the filler is a composite foamcomprising an inorganic foam obtained from a phosphorus-containing acidmaterial (a), a curing agent (b) and, optionally, a blowing agent (c),and an organic foam obtained from a urethane prepolyrner having NCOgroups (d), and water (e), and wherein the flexible material has aflexibility of from 10 mm to 35 mm as measured by the deflection at thecenterpoint of a 500 mm span of a 600×300 mm section of the flexiblematerial having a thickness of 40 mm.
 13. The flexible materialaccording to claim 12, wherein the honeycomb body comprises a metal, aresin-impregnated honeycomb, or a flame-retardant paper honeycomb, ofwhich an incineration residue in the test stipulated in JIS-P8128 is atleast 40%.
 14. The flexible material according to claim 13, comprising aflame-retardant paper honeycomb which is a flame-retardant paperhoneycomb comprising magnesium silicate or aluminum hydroxide in anamount of at least 40 wt %.
 15. The flexible material according to claim12, wherein the phosphorus-containing acid material (a) is at least onemember selected from the group consisting of phosphoric acid,phosphorous acid, phosphoric anhydride, condensed phosphoric acids,polyvalent metal salts thereof, and salts of a water-soluble amine withpolyvalent metal salts.
 16. The flexible material according to claim 12,wherein the phosphorous-containing acid material (a) is a salt of anacid polyvalent metal phosphate with a water-soluble amine.
 17. Theflexible material according to claim 12, wherein the curing agent (b) isat least one member selected from the group consisting of a carbonate(b1), a metal oxide and/or a metal hydroxide (b2), and a light metal(b3) which generates a gas when reacted with an acid or an alkali. 18.The flexible material according to claim 12, wherein the curing agent(b) is at least one of a metal oxide or a metal hydroxide (b2), and theblowing agent (c) is at least one of a low boiling point organic solventor an organic compound which generates a gas by thermal decomposition.19. A sandwich structure which comprises the flexible material of claim12, and one or more surface materials bonded to both sides of theflexible material.
 20. The material of claim 12, wherein thephosphorous-containing acid material is a magnesium primary phosphateand the curing agent is a basic magnesium carbonate.
 21. The material ofclaim 12, wherein the honeycomb body has a cell size of from 5 to 50 mm.22. The material of claim 12, wherein the weight ratio of the inorganicfoam to the organic foam is from 3:1 to 50:1.
 23. The material of claim12, wherein the phosphorous-containing acid material (a) is present inan amount of from 3 to 20 wt % in the inorganic foam.